Methods and devices for accessing a drive train of a wind turbine with elastic coupling, wind turbine and methods

ABSTRACT

Methods and devices for accessing a drive train for a wind turbine utilize an elastic coupling. The drive train comprises a rotor shaft configured to be driven by a rotor about a main axis and a support structure including a bearing housing surrounding at least one bearing and supporting the rotor shaft for rotation about the main axis to constrain other movements of the rotor shaft. A gearbox input shaft and housing supports the gearbox input shaft for rotation while constraining other movements of the gearbox input shaft. The gearbox input shaft is coupled to the rotor shaft by an elastic coupling comprising a first coupling part rigidly connected with the rotor shaft, a second coupling part rigidly connected with the gearbox input shaft, and elastic elements positioned between the first and second coupling part to provide a single joint between the rotor shaft and the gearbox input shaft.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a United States National Phase application of PCT Application No. PCT/EP2016/077732 filed on Nov. 15, 2016, which claims priority to EP 15 194 639.9 filed on Nov. 15, 2015.

FIELD OF INVENTION

The present invention relates to device and methods for accessing a drive train for wind turbines, wind turbines and methods of manufacturing or retrofitting wind turbines.

BACKGROUND

Wind turbines or wind power plants comprise a drive train, which extends from the rotor or rotor hub to the generator. The drive train can comprise a hub, a rotor shaft (or main shaft) a gearbox input shaft, a gearbox and a generator. The drive train is mainly configured to transfer torque from the rotor to the generator. However, there are also other rotor loads different than the mere torque load. These other loads should be transferred to and eliminated by the nacelle structure. The load path of these other loads through the drive train to the nacelle structure depends on the particular arrangement and on variations and magnitudes of these loads, the machining tolerances, load deformations, thermal effects and other conditions. All this may result in undesirable parasitic forces that have the potential to damage elements in the drive train, particularly the gearbox components and the main bearings Eliminating these parasitic forces is inseparably connected with gearbox and bearing reliability.

WO 2012/052022 A1 discloses a drive train for a wind turbine comprising a main shaft and a gearbox with a gearbox input shaft driven by the main shaft. There are two couplings located between the main shaft and the gearbox input member of the gearbox. The two couplings are configured such that the transmission of undesired loads is reduced.

WO 2013/007322 A1 discloses a drive train comprising a rotor shaft and a generator input shaft which are coupled with each other via a coupling having elastic elements. It is disclosed that the coupling comprises two coupling parts which are rigidly connected with the rotor shaft and the generator shaft. However, the elastic elements provided between the coupling parts have chambers filled with a fluid, in particular a hydraulic fluid and they are arranged in pairs.

One of the main drawbacks of an elastic coupling is the potential wear or generally a change of the properties of the elastic coupling during operation. In order to perform maintenance tasks, it can be become necessary to access the inside of the coupling, for example for re-checking the preload of the bolted joints between the coupling and the shafts, access the central pipe which comprises the energy supply for the rotor hub or other maintenance work.

Typically, access to the coupling is possible through the rotor hub and the main shaft. However this is quite time consuming, as the service technician needs to leave the nacelle, enter the hub and move through a narrow space inside the rotor shaft until he reaches the center of the coupling. It is also quite uncomfortable to carry equipment through this access way.

SUMMARY

It is an object of the invention to simplify and improve the access to a drive drain of a wind turbine.

According to an aspect, a drive train for a wind turbine is provided. The drive train comprises a rotor shaft (main shaft) configured to be driven by a rotor about a main axis; a support structure including a bearing housing surrounding at least one bearing and supporting the rotor shaft for rotation about the main axis, thereby constraining other movements of the rotor shaft; a gearbox input shaft and a gearbox housing supporting the gearbox input shaft for rotation about the main axis while constraining other movements of the gearbox input shaft; and an elastic coupling, wherein the gearbox input shaft is coupled to the rotor shaft by the elastic coupling, the elastic coupling comprising a first coupling part rigidly connected with the rotor shaft, a second coupling part rigidly connected with the gearbox input shaft and elastic elements positioned between the first coupling part and the second coupling part, thereby constituting a single joint between the rotor shaft and the gearbox input shaft. A coupling housing and/or the bearing housing can comprise an opening for accessing an inner space of the coupling housing and/or bearing housing.

In an advantageous aspect of the invention, the first coupling part and/or the second coupling part comprises an opening that coincides with the opening of the coupling housing and/or the main bearing housing in a predetermined locked position of the rotor shaft such that an inner space of the first coupling part and/or the second coupling part is accessible.

In another advantage aspect, the opening in the bearing housing and/or the coupling housing is configured to provide access to the elastic elements of the elastic coupling for assembling, disassembling or maintenance.

In still another aspect, the coinciding openings (of the bearing and/or coupling housing and the respective coupling part) are dimensioned as a manhole in order to allow a service technician to pass the openings.

Accordingly, the main bearing housing, the coupling housing and the coupling parts are configured and arranged such that access is directly provided from the nacelle of the wind turbine to the inner side of the elastic coupling via openings in the fixed housings and openings in the rotating parts that coincide when the rotor of the wind turbine is locked in a predetermined position. This access can be used as a manhole and also to carry heavy equipment through the openings, for example by help of an onboard crane. Furthermore, the coinciding openings can also provide access to elastic elements of the elastic coupling for maintenance purposes. According to these aspects, the maintenance work in the wind turbine can be performed in much more efficient and safe manner.

The present invention also provides a method of accessing an elastic coupling of a drive train of wind turbine. The method can comprise at least the steps of: locking a rotor shaft of the drive train in predetermined position, and accessing the elastic coupling through openings coinciding in the predetermined position.

According to the aspects of the invention, in particular due to the described openings, it is also possible for a technician to get access to the hub through the elastic coupling (first part of the elastic coupling) and the rotor shaft.

At least one or all of the elastic elements can be configured and/or arranged such that a force-deformation behavior of the elastic element(s) is different in a first load direction than in a second load direction or any other load direction other than the first load direction.

At least one or all of the elastic elements can be configured and/or arranged such that at least one or all of the elastic element(s) have a first stiffness in a first load direction (dominant direction of stiffness) and a second stiffness in a second load direction. The first stiffness is advantageously greater than the second stiffness. The first stiffness can be greater than any stiffness of the elastic element in other load directions (other than the dominant direction of stiffness).

The elastic element advantageously provides the first stiffness in the main load torque directions. In the context of this specification, a torque or load torque or load torque direction is represented and described by the rotational direction instead of the vector representation, as the referral to the rotational directions is considered more intuitive.

At least one or all of the elastic elements can comprise or be made of rubber, polymer, elastic material or combinations of rubber and/or polymer and/or elastic material and/or stiff components. At least one or all of the elastic elements can be configured or be made in form of springs, helical springs, and/or coil springs. At least one or all of the elastic elements can have the form of pads, cylinders, or cubicles.

Advantageously, at least one or all of the elastic elements can have one dominant axis or dominant dimension or dominant direction in which the stiffness is higher than in any other dimension or axis of the elastic element. The main load direction (main load torque direction) of the drive drain advantageously coincides with the dominant axis or dominant dimension or dominant direction of greatest stiffness of the elastic elements. The axis or dimension of the greatest stiffness of the elastic elements advantageously corresponds to a direction of compression of the elastic element.

The elastic coupling can be configured to allow a relative rotation between the first and the second coupling part around axes perpendicular to the main axis, a translation along the main axis as well as a translation in the axes perpendicular to the main axis more easily than a relative rotation of the first coupling part and the second coupling part with respect to each other in the load torque direction around the main axis. In other words, the elastic elements in the elastic coupling, in particular the stiffness of the elastic elements, are configured such that the elastic coupling allows the above movements more easily than any relative movement of the two coupling parts in the torque load direction (s)

The elastic elements can be arranged and configured such that the elastic elements provide different stiffness characteristics per load direction. The transfer of the torque can be performed with a first stiffness (in the dominant direction of stiffness). The elastic elements can be configured to provide a second stiffness with respect to movements in transverse degrees of freedom and rotational degrees of freedom except for a rotation around the longitudinal direction of the main axis. This allows the first coupling part and the second coupling part to be offset and deflected with respect to each other without generating significant reaction forces.

In an advantageous aspect, only a single elastic element is used for a first, positive load torque direction (i.e. in a first direction of rotation) and a second, negative load torque direction (i.e. in a second direction of rotation, opposite to first direction of rotation). The first load torque direction is opposite to the second load torque direction.

In an embodiment using a single elastic element for both torque directions, each elastic element can be arranged such that (congruent) attachment, abutment or pushing surfaces of the first coupling part and the second coupling part are at each side of the elastic element such that the elastic element can be loaded in a positive torque direction as well as in a negative torque direction. In particular, the elastic elements and the first and second coupling part are configured such that the elastic elements are compressed along their dominant direction and/or dominant axis of stiffness in the first load torque direction and in an opposite, second load torque direction. This aspect reduces the number of required elastic elements, simplifies manufacturing and maintenance and reduces costs.

Accordingly, in an aspect, only a single elastic element for two opposite torque load directions is used. All the elastic elements of the elastic coupling can be used for the two opposite torque loads. The first coupling part can provide at least a first attachment (or abutment, or pushing) surface and an opposite second attachment (or abutment or pushing) surface. The second coupling part can then also provide at least a first attachment (or abutment or pushing) surface and an opposite second attachment (or abutment or pushing) surface.

One attachment (or abutment) surface of each of the two coupling parts can be in contact with a same first side of an elastic element and one attachment (or abutment) surface of each of the first and the second coupling part can be in contact with a same second side of the elastic element. The second side of the elastic element is opposite to the first side of the elastic element. The attachment (or abutment) surfaces of the first and the second coupling part being in contact with the same side of the elastic element can be referred to as “congruent”. In an embodiment, the abutments surfaces can be provided by superposed or coinciding windows in the coupling parts. However, there are various different possible configurations. One minimum requirement is that each of the two opposite sides of the elastic element should at least be arranged to be pushed (or abut against) an abutment or attachment or contact surface of both, the first and the second coupling part. The elastic elements can be located on congruent attachment/abutment surfaces of the first and the second coupling part such that a single elastic element can be loaded in a positive torque direction as well as in a the negative torque direction. The respective surfaces of the two coupling parts on one side of the elastic element can be arranged side by side and adjacent to each other. It is also possible that the two surfaces are provided by different coupling parts and that the surface of one coupling part is arranged behind a shoulder or extension of the respective other coupling part. However, the last embodiment can advantageous for embodiments not requiring pre-stressed elastic elements.

The previously described aspects provide that a single elastic element can be used for two opposite load torque directions, i.e. the positive torque direction and the negative torque direction. The elastic element is than only compressed or squeezed along the dominant axis or direction of stiffness regardless of the load torque direction. The number of required elastic elements EM can then be reduced to half the number of embodiments using pairs of modules.

In an aspect, if the elastic elements use a chamber for fluid for adjusting the stiffness of the elastic elements, all the elastic elements can be hydraulically coupled with each other. It is not necessary to separate the hydraulic connection into one system for positive load torque and one system for negative load torque.

In an aspect, pairs of elastic elements can be located between respective opposite attachment surfaces of the first coupling part and the second coupling part such that a first element of each pair is loaded in a first/positive torque direction and a second element of each pair is loaded in a second/negative torque direction. The second torque direction is opposite to the first torque direction. More specifically, the elastic elements can be arranged in pairs of two adjacent elastic elements along a circumference of the elastic coupling between abutment surfaces of the same coupling part, such that the pairs of the elastic elements can be located between respective opposite attachment surfaces of the first coupling part or the second coupling part such that a first element of each pair is loaded in a first/positive torque direction and a second element of each pair is loaded in a second/negative torque direction, wherein the second torque direction is opposite to the first torque direction.

In an aspect, the rotor shaft and the gearbox input shaft can be mounted/assembled with a preset eccentricity of their longitudinal main axes, such that a longitudinal axis of the rotor shaft and a longitudinal axis of the gearbox input shaft are initially mounted eccentrically to each other in order to minimize any eccentricity or offset resulting from weight and/or loads and/or torque during operation. The relevant torque could be the normal expected torque during operation of the wind turbine. In order to achieve the preset eccentricity the center point of the bearing housing may be slightly shifted. The center point of the bearing housing may be shifted vertically. This has an influence on the bending line such that in total undesired eccentricities are compensated by the preset eccentricity during mounting and assembly of the wind turbine/drive drain.

Regarding the previously described aspect, it is normally most advantageous that the rotor shaft and the gearbox input shaft of a drive drain of a wind turbine are perfectly aligned and centered with respect to each other. Otherwise, any coupling and in particular an elastic coupling, specifically the elastic elements, as described herein, will be constantly agitated during each rotation. This can substantially increase the wear of the elastic elements. According to this aspect, the rotor shaft and the gearbox input shaft are arranged with respect to each other with a slight eccentricity in order to compensate any other effects that introduce an opposite eccentricity. If for example the coupling housing, the gearbox housing and the generator are all freely suspended from the bearing housing, this can introduce a slight eccentricity between the rotor shaft and the gearbox input shaft which results in an eccentricity in the elastic coupling, in particular an eccentricity of the first coupling part with respect to the second coupling part. This and any other eccentricity can then be compensated by the suspension of the bearing housing, in particular the suspension of the main bearing in the bearing housing. The bearing housing may be coupled to the main frame of the nacelle. The ring flange between the bearing housing and coupling housing can be used to create the eccentricity between the rotor shaft and the gearbox input shaft. The eccentricity can also or in combination be created by the coupling (flange) the coupling housing and the gearbox housing. An advantageous direction is an eccentricity in a vertical direction. It is also possible to create the eccentricity in any other directions, as for example the horizontal direction. The eccentricity is advantageously in the range of less than 1 mm. The eccentricity provides that during each rotation the elastic elements are not agitated. Since the gearbox (housing) and the generator (housing) are suspended from the bearing housing, the weight of these components can introduce an eccentricity that is to be compensated by a predetermined and preset eccentricity in the opposite direction. Accordingly, and expected or determined eccentricity can be can be compensated by a slight preset eccentricity introduced by a shift of the bearing housing.

The elastic elements can generally be positioned circumferentially and in a tangential direction between (for example respective abutment, attachment, or pushing surfaces of) the first coupling part and the second coupling part of the elastic coupling and the first coupling part and the second coupling can provide attachment, abutment and/or pushing surfaces for opposite ends of each of the elastic elements.

At least one or all of the elastic elements can be pre-stressed (squeezed, compressed) in a non-loaded condition in order to increase the stiffness in a specific load direction. In particular, the torsional stiffness can be increased by pre-stressing the elastic elements. The stiffness is advantageously increased in the main load torque direction which can then correspond to the dominant axis and/or the dominant direction of stiffness of the elastic elements.

At least one of the elastic elements can contain a chamber configured to be filled with a fluid. Advantageously, a plurality of the elastic elements can contain a chamber configured to be filled with a fluid. The chambers can be hydraulically connected with each other.

The chambers of all elastic elements acting in the positive torque direction can be hydraulically coupled with each other and the chambers of all the elastic elements acting in the negative torque direction can be hydraulically coupled with each other.

The invention also provides a wind turbine comprising the drive drain according to the aspects and embodiments of the invention. The invention further provides a wind park comprising a wind turbine comprising a drive drain according to the aspects and embodiments of the invention.

The invention also provides a method for manufacturing and/or for retrofitting a wind turbine comprising a drive drain according to the aspects and embodiments of the invention.

BRIEF DESCRIPTION OF DRAWINGS

Further features and advantages of the invention will ensue from the following description with reference to the accompanying drawings, wherein

FIG. 1 is simplified representation of a part of a drive drain according to an embodiment,

FIG. 2 is a simplified perspective view on an elastic coupling according to an embodiment,

FIG. 3 is a simplified cross-sectional view of a part of the drive drain shown in FIG. 1 according to an embodiment,

FIG. 4 is a simplified perspective view on a part of the drive drain shown in FIG. 1 and FIG. 3 according to an embodiment,

FIG. 5 is a simplified detailed view of an access opening to an elastic element,

FIG. 6 is a simplified cross-sectional view of a part of the drive drain shown in FIG. 1 according to an embodiment,

FIG. 7 is a simplified cross-sectional view along line A-A in FIG. 1 of an elastic coupling according to an embodiment,

FIG. 8 is a simplified cross-sectional view along line A-A in FIG. 1 of an elastic coupling according to an embodiment in a first load condition,

FIG. 9 is a simplified cross-sectional view along line A-A in FIG. 1 of an elastic coupling according to an embodiment in a second load condition,

FIG. 10 is a simplified cross-sectional view along line A-A in FIG. 1 of an elastic coupling according to an embodiment in a third load condition,

FIG. 11 is substantially similar to FIG. 8 including an additional detail,

FIG. 12 is a simplified cross-sectional view of a part of the embodiments shown in FIGS. 8 to 10 using a single elastic element,

FIG. 13 is a simplified cross-sectional view of a part of the embodiments shown in FIGS. 8 to 10 using a single elastic element,

FIG. 14 is a simplified perspective view on an elastic element according to an embodiment, and

FIG. 15 is a simplified perspective view on an elastic element according to an embodiment.

FIG. 16 shows a simplified side view of a part of the drive drain of a wind turbine according to an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is simplified representation of a part of a transmission system 1 according to an embodiment. The transmission system 1 comprises a hub 2, a rotor shaft (or main shaft) 3, a main bearing 4, a main bearing housing 5, a gearbox input shaft 6, a gearbox 7 with a gearbox housing 8 and a generator 9. Between the rotor shaft 3 and the gearbox input shaft 6 is the elastic coupling 10. The elastic coupling 10 comprises a first coupling part 11 and a second coupling part 12. The elastic coupling 10 has a coupling housing 15.

FIG. 2 is a simplified perspective view on an elastic coupling 10 according to an embodiment. The elastic coupling 10 comprises the first coupling part 11 and the second coupling part 12. The first coupling part 11 has a flange 13 by which it can be rigidly coupled to the rotor shaft 3. The second coupling part 12 has a flange 14 by which it can be rigidly coupled to the gearbox input shaft 6. The first coupling part 11 is coupled to the second coupling part 12 by a plurality of elastic elements EM1 to EM10 (EM7 and EM8 are not visible in this perspective). The elastic elements EM1 to EM10 are evenly distributed along a circumferential direction of the first coupling part 11 and the second coupling part 12. Although the present embodiment shows ten elastic elements EM1 to EM10, any number of elastic elements can be used in other embodiments.

FIG. 3 is a simplified cross-sectional view of a part of the drive drain 1 shown in FIG. 1 according to an embodiment. There is a first opening O1 in the main bearing housing 5 and a second opening O2 in the first coupling part 11 of the elastic coupling 10. In the shown position of the rotor shaft 3, the two openings O1 and O2 coincide. The openings O1, O2 are both large enough to provide access to a service technician ST to the interior space of the elastic coupling 10. The interior space of the elastic coupling 10, i.e. the space between the first coupling part 11 and the second coupling part 12 is large enough to accommodate the service technician ST. The service technician ST can now access an elastic element EM of the elastic coupling 10. The openings O1, O2 are dimensioned as manholes, being large enough to allow a service technician to pass through them and reach the interior space of the elastic coupling.

Furthermore, due to the described openings O1, O2, it is also possible for a technician to get access to the hub 2 through the elastic coupling 10 (first part of the elastic coupling 11) and the rotor shaft 3.

FIG. 4 is a simplified perspective view on a part of the drive drain 1 shown in FIG. 1 and FIG. 3 according to an embodiment. The service technician is located in the opening O1 in the main bearing housing 5. There are further openings O3, O4, O5 in the coupling housing 15. In a predetermined locked position of the rotor shaft 3, these openings O3, O4, O5 grant access to the elastic elements of the elastic coupling 10. This is shown in more detail in FIG. 5. The openings O3, O4, O5 can have a rather circular or rectangular shape. In the present embodiment the openings have a rather rectangular shape. The maximum diameters DM1 and DM2 can then have the following advantageous dimensions. DM1 can be 400 mm to 600 mm, advantageously about 450 mm. The diameter DM2 can also be 400 mm to 600 mm, advantageously about 500 mm. Any opening in any of the housings may have a minimum diameter of 400 mm, more advantageously, the diameter of any opening should at least be 500 mm. For openings being configured to provide access for a service technician, the minimum diameter of any such opening can be greater than 600 mm.

FIG. 5 is a simplified detailed view of an access opening O4 to an elastic element EM of the elastic coupling. Also in this situation, there are coinciding openings in the coupling housing 15 and in the coupling parts of the elastic coupling 10. The elastic element EM is partly lifted already towards the opening O4 in order to be replaced or checked. Likewise, it is possible to insert an elastic element EM through the opening O4.

FIG. 6 is a simplified cross-sectional view of a part of the drive drain 1 shown in FIG. 1 according to an embodiment. In this embodiment, the opening O2 in the first coupling part 11 and an opening in the main bearing housing are such that the service technician ST can access the main bearing 4. This aspect is advantageous for maintaining or replacing, for example a sealing of the main bearing 4.

FIG. 7 is a simplified cross-sectional view of an elastic coupling 10 along line A-A in FIG. 1 according to the embodiment shown in FIG. 1 and FIG. 2. The elastic elements EM1 to EM10 are substantially evenly distributed along a circumferential direction CD. In this embodiment, the elastic elements EM1 to EM10 are arranged in pairs of two elastic elements: EM1 and EM2, EM3 and EM4, EM5 and EM6, EM7 and EM8 as well as EM9 and EM10. Accordingly, there are five pairs of elastic elements. There is always a circumferential section CS1 to C10 of one of the first or second coupling part 11, 12 between adjacent elastic elements. Circumferential sections CS1, CS3, CS5, CS7 and CS9 belong to the first coupling part 11. Circumferential sections CS2, CS4, CS6, CS8 and CS10 belong to the second coupling part 12. Accordingly, each elastic element E1 to E10 is located between a circumferential section of the first coupling part 11 and a circumferential section of the second coupling part 12. The circumferential sections CS1 to CS10 provide attachment surfaces AS for the elastic elements EM1 to EM10 on opposite ends of the each elastic element EM1 to EM10.

The circumferential direction CD is also the direction of the torque load. However, the torque load can have a first direction LDP or a second direction LDN which are opposite to each other. In the present context, a torque or load torque or load torque direction is represented and described rather by the rotational direction than by the vector representation, as the referral to the rotational directions is considered more intuitive.

FIG. 8 is a simplified cross-sectional view of an elastic coupling 10 along line A-A in FIG. 1 in a first load condition according to an embodiment. This embodiment of an elastic coupling 10 differs from the previous one in that each of the elastic elements EM1 to EM4 is configured and arranged such that the elastic elements EM1 to EM4 can be loaded in positive torque direction LDP as well as in the negative torque direction LDN. The first coupling part 11 and the second coupling part 12 are represented as disks having superposed windows W through which each of the elastic elements EM1 to EM4 protrudes. The first coupling part 11 is represented in dashed lines while the second coupling part 12 is represented by solid lines. The shown load condition is an undeflected situation such that no torque load is applied and the rotor shaft 3 and the gearbox input shaft 6 and therefore the coupling parts 11, 12 are not misaligned.

FIG. 9 is a simplified cross-sectional view of the an elastic coupling 10 along line A-A in FIG. 1 (similar to the embodiment of FIG. 8) in a second load condition. In this load condition, load torque is applied to the elastic coupling 10 but the axes of the gearbox input shaft and the rotor shaft are still well aligned.

FIG. 10 is a simplified cross-sectional view of the an elastic coupling 10 along line A-A in FIG. 1 (similar to the embodiment of FIG. 8 and FIG. 9) in a third load condition. In this load condition load torque is applied and the main axes are misaligned.

FIG. 11 is substantially similar to FIG. 8 including an additional detail. This embodiment uses elastic elements EM1 to EM4 which are also referred to as hydraulic rubber elements or hydraulic elastomers etc. (more details of such an element are described with respect to FIG. 15). These elements have an inner chamber that can be filled with a fluid in order to adjust the stiffness (for example torsional stiffness). The elastic elements or rather the chambers of the elastic elements are coupled to a hydraulic circuit. If only a single elastic element EM1 to EM4 can be used for both load torque directions, as described herein, a single hydraulic circuit HYD can be used for all elements EM1 to EM4 instead of two separate hydraulic circuits for the elastic elements of each load torque direction.

FIG. 12 is a simplified cross-sectional view of a part of the embodiments shown in FIGS. 8 to 10 using a single elastic element EM for two opposite torque load directions. Each of the elastic elements (in FIG. 8 to 10) can be the elastic element EM shown in FIG. 11. The first coupling part 11 provides at least a first attachment (or abutment) surface AS1_11 and an opposite second attachment (or abutment) surface AS2_11. The second coupling part 12 also provides at least a first attachment (or abutment) surface AS1_12 and an opposite second attachment (or abutment) surface AS2_12. In this embodiment, one attachment (or abutment) surface AS1_11, AS1_12 of each of the two coupling parts 11, 12 is in contact with a same first side EMFS of the elastic element and one attachment (or abutment) surface AS2_11, AS2_12 of each of the two coupling parts 11, 12 is in contact with a same second side EMSS of the elastic element. The second side EMSS of the elastic element EM is opposite to the first side EMFS of the elastic element. In an embodiment, the abutments surfaces AS1_11, AS2_11, AS1_12, AS2_12 can be provided by superposed or coinciding windows W11, W12 in the coupling parts. However, there are various different possible configurations. A minimum requirement is that each of the two opposite sides EMFS, EMSS of the elastic element should at least abut against an abutment or attachment or contact surface of both, the first and the second coupling part 11, 12. In other words, the elastic elements are located on congruent attachment/abutment surfaces of the first and the second coupling part such that a single elastic element is loaded in a positive torque direction as well as in a the negative torque direction.

This provides that a single elastic element EM can be used for both, opposite load torque direction, i.e. the positive torque direction LDP and the negative torque direction LDN. The elastic element is than only compressed or squeezed along the dominant axis or direction of stiffness regardless of the load torque direction. The number of required elastic elements EM can then be reduced to half the number of embodiments using pairs of modules.

In an aspect, if the elastic elements use a chamber for fluid for adjusting the stiffness of the elastic elements, all the elastic elements can be hydraulically coupled with each other. It is not necessary to separate the hydraulic connection into one system for positive load torque and one system for negative load torque.

FIG. 13 is a simplified cross-sectional view of a part of the embodiments shown in FIGS. 8 to 11 using a single elastic element EM for two opposite torque load directions according to another embodiment. In this embodiment, the elastic element EM is only held between one abutment, attachment and/or pushing surface (or shoulder) AS11 of the first coupling part 11 at one end of the elastic element EM and one abutment, attachment and/or pushing surface (or shoulder) AS12 of the second coupling part 12 at another, opposite end of the elastic element EM. However, the respective abutment surface AS11 and A12 of each coupling part 11, 12 extends over and covers the respective other coupling part. This embodiment is advantageous if the elastic element EM does not need to be pre-stressed.

FIG. 14 is a simplified perspective view on an elastic element EM to be used for the embodiments and aspects described herein. The dominant direction D1 is the direction of a force (due to torque) in which the elastic element EM has the greatest stiffness. It should be noted that the elastic element EM is supposed to be compressed or squeezed in the dominant direction D1. Just as examples other directions D2, D3 of potential forces are also indicated. The elastic element EM has a lower stiffness in the directions D2 and D3 and any other direction different than D1.

In still other words, any elastic element EM has a dominant axis of stiffness DA and a dominant direction of stiffness D1 lying in the dominant axis of stiffness DA. The dominant direction of stiffness D1 is advantageously a direction in which the elastic element EM is compressed. The stiffness of the elastic element EM is greater in the dominant direction of stiffness D1 than in any direction relative to the elastic element EM different from the dominant direction D1.

FIG. 15 is a simplified perspective view on an elastic element EM that can be used in connection with the aspects and embodiments of the invention. Generally, at least one or all of the elastic elements can comprise or be made of rubber, polymer, elastic material or combinations of rubber and/or polymer and/or elastic material and/or stiff components. At least one or all of the elastic elements can be configured or be made in form of springs, helical springs, and/or coil springs. At least one or all of the elastic elements can have the form of pads, cylinders, or cubicles.

The elastic element EM shown in FIG. 15 is generally made of an elastic material (like rubber or polymers etc.) and comprises an inner chamber CH (dashed lines) that can be filled with a fluid in order to adjust the stiffness. The elastic element EM can further comprise inlet and outlets for the fluid. In this embodiment, there is a radial inlet/outlet IN_OUT_R and a tangential inlet/outlet IN_OUT_T. Furthermore, there is a fluid access FA and a pressure sensor SENS for determining the pressure in the chamber CH of the elastic element EM.

The elastic element EM can also be referred to as rubber hydraulic element. It can have a pitch cycle diameter of 2300 mm, a weight of 38 kg and provide a high torsional stiffness in the dominant direction. It further provides a low axial and lateral stiffness, i.e. in directions other than the dominant direction. The elastic element can operate with a hydraulic pressure of max. 600 bar. It can be hydraulically coupled with other elastic elements of a similar type through hoses or tubes (hydraulic circuit). The working pressure of these tubes or hoses can be 1040 bar, while the minimum burst pressure could be 2600 bar.

FIG. 16 shows a simplified side view of a part of the drive drain 1 of a wind turbine according to an embodiment. There is a main frame 16 (supporting structure of a nacelle (not shown) of a wind turbine (not shown). The drive drain comprises a rotor shaft (or main shaft) 3 which is held by the main bearing 4 (not shown) in the bearing housing 5. Only the bearing housing 5 is suspended from or carried by the main frame 16. The coupling housing 15 including the elastic coupling 10, the gearbox housing 8 including the gearbox input shaft 6 and the gearbox 7 as well as the generator 9 are only suspended from the bearing housing 5. They all extend freely over the main frame 16. The entire weight of the elastic coupling 10, the gearbox, and the generator 9 including all their housings and internal parts can introduce an eccentricity between the rotor shaft 3 and the gearbox input shaft 6.

In an embodiment, a longitudinal axis A3 of the rotor shaft 3 and a longitudinal axis A6 of the gearbox input shaft 6 are then mounted/assembled with a predetermined and preset eccentricity EXC with respect to each other in order to minimize the offset/eccentricity resulting from, for example weight and/or other loads and/or other effects. Normally, it is most advantageous that the rotor shaft 3 and the gearbox input shaft 6 of a drive drain 1 of a wind turbine are perfectly aligned and centered with respect to each other. Otherwise, any coupling and in particular an elastic coupling 10, more specifically the elastic elements EM of the elastic coupling 10, as described herein, can be constantly agitated/worked through during each rotation. This can substantially increase the wear of the elastic elements EM. According to the present embodiment, the rotor shaft 3 and the gearbox input shaft 6 are arranged with respect to each with a slight eccentricity in order to compensate any other effects that introduce an opposite eccentricity. If for example the coupling housing 15, the gearbox housing 8 and the generator 9 are all freely suspended from the bearing housing 5, this can introduce a slight eccentricity between the rotor shaft 3 and the gearbox input shaft 6 which results in an eccentricity in the elastic coupling 10, in particular an eccentricity of the first coupling part 11 with respect to the second coupling part 12. This and any other eccentricity can then be compensated, for example by the suspension of the bearing housing 5, in particular the suspension of the main bearing 4 in the bearing housing 5. The bearing housing 5 may be coupled to the main frame 16 of the nacelle by an annular (ring-shaped) flange (not shown). This flange can be used to create the eccentricity between the rotor shaft 3 and the gearbox input shaft 6. In particular, the center point of the bearing may be shifted during mounting/assembly. An advantageous direction is a preset eccentricity in a vertical direction V. It is also possible to create the preset eccentricity in any other directions, as for example the horizontal direction H. The preset eccentricity is advantageously in the range of less than 1 mm. The preset eccentricity provides that the elastic elements EM are not or less agitated during each rotation. Since the gearbox 7 (housing) and the generator 9 (housing) are suspended on the bearing housing 5, the weight of these components can introduce an eccentricity that is to be compensated by a predetermined and preset eccentricity in the opposite direction. Accordingly, an expected or determined eccentricity can be compensated by a slight preset and compensating (for example opposite) eccentricity introduced by a shift of the bearing housing 5. The preset eccentricity of the longitudinal main axes of the rotor shaft and the gearbox input shaft can be used to compensate and/or minimize any eccentricity or offset resulting from weight and/or loads and/or torque. The relevant torque could be the normal expected torque during operation of the wind turbine. In order to achieve the preset eccentricity the center point of the bearing housing may be slightly shifted. The center point of the bearing housing may be shifted vertically. This has an influence on the bending line such that in total, the undesired eccentricities are compensated by the preset eccentricity during mounting and/or assembling of the wind turbine/drive drain.

The aspects and embodiments of the invention are particularly synergetic, as the elastic coupling 10 requires maintenance of the elastic elements. The openings provide access to these elements. Furthermore, the openings may also grant access to hydraulic circuits, tubes or hoses of any hydraulic parts or sensors provided in the elastic coupling. All these parts can be accessed and maintained or exchanged. The term “coinciding” openings can be interpreted as precisely overlapping, lying one above another or being precisely superposed.

This means that any opening can be made just large enough to allow the respective measure to be taken (technician to pass or elastic element to be accessed, retrieved from or inserted into the elastic coupling).

Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further alternatives will occur to the skilled person that lie within the scope of the invention as claimed 

The invention claimed is:
 1. A drive train for a wind turbine comprising: a rotor shaft configured to be driven by a rotor about a main axis; a support structure including a bearing housing surrounding an at least one bearing and supporting the rotor shaft for rotation about the main axis, thereby constraining other movements of the rotor shaft; a gearbox input shaft and a gearbox housing supporting the gearbox input shaft for rotation about the main axis while constraining other movements of the gearbox input shaft; and an elastic coupling, wherein the gearbox input shaft is coupled to the rotor shaft by the elastic coupling, the elastic coupling comprising a first coupling part rigidly connected with the rotor shaft, a second coupling part rigidly connected with the gearbox input shaft, and elastic elements distributed along a circumferential direction around the first coupling part and the second coupling part to connect the first coupling part to the second coupling part, thereby constituting a single joint between the rotor shaft and the gearbox input shaft, wherein the elastic coupling comprises an opening that coincides with an opening of the coupling housing and/or bearing housing in a predetermined locked position of the rotor shaft such than an inner space of the elastic coupling is accessible.
 2. The drive train according to claim 1, wherein the first coupling part and/or the second coupling part comprises an opening that coincides with the opening of the coupling housing and/or the main bearing housing in a predetermined locked position of the rotor shaft such that an inner space of the first coupling part and/or the second coupling part is accessible.
 3. The drive train according to claim 1 or 2, wherein the opening in the bearing housing and/or the coupling housing is configured to provide access to the elastic elements of the elastic coupling for assembling, disassembling or maintenance.
 4. The drive train according to claim 2 or 3, wherein the coinciding openings are dimensioned as a manhole in order to allow a service technician to pass the openings.
 5. The drive train according to anyone of the previous claims, wherein the opening in the main bearing housing and/or the coupling housing is configured to provide access to a sealing of the main bearing for maintenance purpose.
 6. The drive train according to anyone of the preceding claims, wherein the elastic elements are configured such that the elastic elements have a first stiffness in a first load direction and a second stiffness in a second load direction, the first stiffness being greater than the second stiffness, and the elastic elements are arranged such that a main load torque direction coincides with the first load direction.
 7. The drive train according to anyone of the preceding claims, wherein the rotor shaft and the gearbox input shaft are mounted with a preset eccentricity of their longitudinal main axes, such that a longitudinal axis of the rotor shaft and a longitudinal axis of the gearbox input shaft are initially mounted eccentrically to each other in order to minimize any eccentricity or offset resulting from weight and/or loads and/or torque during operation.
 8. The drive train according to anyone of the preceding claims, wherein the elastic elements are pre-stressed in a non-loaded condition in order to increase a stiffness, in particular a torsional stiffness.
 9. The drive train according to anyone of the preceding claims, wherein each of the elastic elements contains a chamber configured to be filled with a fluid and at least some of the chambers are hydraulically connected with each other.
 10. A wind turbine comprising the drive train according to anyone of the preceding claims.
 11. A wind park comprising a wind turbine according to claim
 10. 12. A method of manufacturing or retrofitting a wind turbine according to claim
 10. 13. A method of accessing an elastic coupling of a drive train of wind turbine, the method comprising the steps of: locking a rotor shaft of the drive train in predetermined position, accessing the elastic coupling through openings of the elastic coupling that coincide with openings of a main bearing housing and/or an elastic coupling housing in the predetermined position. 